How can I turn this pseudo code into a Matlab code?

I want to make a for loop that describes this but I am unsure how to start. I am making a function with the input X.

Pseudo code:

If X is not given,
look for the object 'Hfig4' and extract the data saved under the 'userdata' field.

How can I turn this into matlab code?

[dpb]

What have you tried???

doc nargin
doc findobj

Doesn't seem to be any need for any for loop; an if...end clause, perhaps.